When a lost part of a tooth is filled or covered with a restorative material, generally a dental adhesive is used. A known dental adhesive is one containing a polymerizable monomer having a polymerizable group and a hydroxyl group.
For example, WO 2004/047773 describes a dental adhesive composition characterized by containing a polyfunctional polymerizable monomer that is an ester compound of polyhydric alcohol having 3 to 6 carbon atoms and a plurality of (meth)acrylic acids and that has one to two hydroxyl groups, a monofunctional (meth)acrylate having no hydroxyl group in the molecule, a polymerizable monomer having an acidic group in the molecule, an organoboron compound as a curing agent, and a filler. This describes that the addition of a small amount of the above polyfunctional polymerizable monomer to the composition can improve the cure rate considerably almost without affecting the adhesive properties of the composition, physical properties of the cured product, or operable time. This composition is, however, not necessarily excellent in penetrability into a collagen layer of dentin and may cause a reduction in bond strength, and therefore improvement in this respect has been desired.
When such a dental adhesive is allowed to act on dentin, it is important for the dental adhesive to have a decalcifying effect that allows a dentin surface to be dissolved with an acidic component, a penetration effect that allows a monomer component to penetrate into a collagen layer of dentin, and a curing effect that allows the monomer component thus penetrated to solidify to form a hybrid layer (hereinafter also referred to as a “resin-impregnated layer”) with collagen.
It has been studied so far to simplify the form of application of the dental adhesive from a three-component three-step type in which the aforementioned decalcifying effect, penetration effect, and curing effect are applied sequentially, to a two-component two-step type in which the decalcifying effect and the penetration effect are integrated, and further to a one-component one-step type in which the decalcifying effect, penetration effect, and curing effect are all combined together. All the forms of application require compositions that can be used for dental adhesives that are excellent in adhesive properties. Therefore, there is a demand for a polymerizable monomer that is used as a component of the composition and that imparts the excellent adhesive properties.